Duration: 1/2 Hour – 1 Hour
NGSS 1-PS4-3 Plan and conduct investigations to determine the effect of placing objects made with different materials in the path of a beam of light.
NGSS MS-PS4-2 Develop and use a model to describe that waves are reflected, absorbed or transmitted through various materials.
Shadows are an absence of light. Light travels in a straight line, and when it meets an obstacle, cannot move around it. The light is then either refected, absorbed, or transmitted. If the object is transparent, and the light is transmitted, the light will continue on its path on the other side of the obstacle. If the object is opaque, however, the light is either reflected, absorbed, or both. Either way, the light does not make it to the other side of the object, and a shadow is formed.
Some transparent objects allow only certain wavelengths, or colors, of light to pass through them. This is called selective transmission. A red piece of plastic, like the Reflect View, will allow only red light to pass through it. All other wavelengths of light will be absorbed, or blocked.
We’re now going to use what we know about selective transmission to create shadows using selectively transparent objects.
Place the Reflect View about 5-10 cm from the wall/screen.Start out by shining the red Light Blox at the Reflect View. What happens?
The RED light casts a RED shadow as it passed through the semi transparent Reflect View.
Stand the pencil vertically next to the Reflect View.
Shine the RED light at the pencil on its own. What do you see? Is this what you expected?
Shine the BLUE light at the pencil on its own.What do you see? Is this what you expected?
The pencil casts a shadow on the screen behind it. Regardless of the color of the light, the opaque pencil allowed none of the light to pass through it.
Move the pencil so that it stands between you and the Reflect View.
Shine the red Light Blox at the pencil and the Reflect View together. What do you see on the screen?
You’ll notice that the red light passes through the Reflect View unhindered. The pencil blocks the light, however, and a shadow of the pencil is formed on the screen.
Leave the pencil so that it stands between you and the Reflect View.
Now shine the blue light at the Reflect View and pencil together. What do you see? What happened to the pencil’s shadow?
This time, the entire Reflect View casts a shadow! None of the blue light makes it to the other side of the Reflect View, since the Reflect View absorbed all the blue light, and would only allow red light to pass.